* doc/lispref/internals.texi (Module Values): Clarify that the
truncation is towards negative infinity.
* test/data/emacs-module/mod-test.c (Fmod_test_nanoseconds): Add test
function.
(emacs_module_init): Define it.
* test/src/emacs-module-tests.el (mod-test-nanoseconds): New unit test.